VERNON — Law enforcement diving agencies from three New England states launched an underwater search Tuesday for clues in the disappearance of a New Hampshire woman and her teenage daughter, a cold case from 2001.

Divers from the Vermont State Police, as well as the New Hampshire Fish and Game Dive Team, the New Hampshire State Police Marine Patrol United, and the Massachusetts State Police Underwater Recovery Team, converged on the Vernon hydroelectric dam on the Connecticut River for what is expected to be a two-day search, according to Benjamin Agati, assistant New Hampshire attorney general.

Agati said TransCanada, the owner of the hydro dam, was cooperating by lowering the river level in the area of the search, which is both upstream and downstream of the dam, and immediately downstream from the Vermont Yankee nuclear power station.

Tina Sinclair, 36, and her daughter Bethany, 15, of Chesterfield, a small town across the Connecticut River from Brattleboro, disappeared sometime during the weekend of Feb. 2-3, 2001. Their bodies have never been found. At the time of their disappearance, they lived at the home of Tina Sinclair’s boyfriend, Eugene “Van” Bowman, at 182 Mountain Road in Chesterfield.

The Sinclairs left behind their car and the mother’s cellphone.

Bowman was a former control room operator at Vermont Yankee.

Agati said the searches this week are not based on any new information or leads. Instead, authorities are taking advantage of unspecified “new technologies.”

He said the Connecticut River had been searched in the past in the area where divers focused Tuesday, but they were now relying on new training, techniques and resources. In addition, he said, areas not previously accessible to searchers would be searched.

“We were not able to get this close to the dam before,” he said, adding that searchers were also launching boats from Vermont Yankee’s boat launch area above the dam.

Agati said that a recent case in New York state involved the recovery of a body that had been underwater for decades. “They ended up finding a body 35 or 40 years later,” he said.

Some of the areas near the dam involve swift water, while others are more calm, he said.

Bowman was convicted of aggravated felonious sexual assault in May 2001 involving a young girl. Agati said that Bowman, who was labeled a “person of interest” rather than a suspect in the disappearance of the Sinclairs, is now out of jail and living in Cheshire County in New Hampshire.

According to reports from the time, Bowman told police that he and Tina Sinclair had argued, and he had left his home, and when he returned, they were gone.